1. Field of the Invention
The invention relates to an apparatus for manufacturing a multi-layered wiring board, and more particularly to an apparatus for manufacturing a multi-layered wiring board having interlayer connection made by conductive pillars. The invention also relates to an apparatus for manufacturing a multi-layered wiring board having conductive pillars formed on a conductive foil and an apparatus for manufacturing a multi-layered wiring board having a conductive foil having conductive pillars laminated with an insulating resin layer.
2. Description of the Related Arts
Demands for high-density mounting of electronic elements are increasing as various types of electronic equipment are made compact and highly advanced in performance. In response to such demands, a type of wiring board, such as printed wiring board being used extensively is a multi-layered wiring board which has a laminated structure with insulating layers and wiring layers alternately overlaid. The multi-layered wiring board has wiring layers overlaid into a multi-layered structure in order to respond to the demands for high density and high performance. Interlayer connection of a plurality of wiring layers has been established by PTH(plated through hole(s)).
The multi-layered wiring board with via holes such as PTHs for interlayer connection of wiring layers has a disadvantage that it is not easy to comply with the demands for high-density mounting.
For example, wiring or mounting of electronic elements cannot be made in an area where a through hole is formed. Therefore, improvement of wiring density and high-density mounting is limited. In these years, wiring of the printed wiring board is also made to have high density as electronic elements are mounted in high density. When through holes are made to have a small diameter to comply with fine patterning of wiring, there is a problem that reliable interlayer connection is hardly assured.
In addition, for the interlayer connection with through holes, a through hole forming step and a plating step are involved, making the manufacturing process lengthy, and it is also disadvantageous in view of productivity.
For example, a step for forming through holes requires to make holes one by one by drilling and takes a long time. Especially, when through holes are drilled so to have a smaller diameter in this step, productivity is extremely lowered. Besides, after forming the through holes, a polishing step for removing burrs and a plating step are required.
Furthermore, positions where through holes are formed are required to be determined with high precision. It is also necessary to consider adhesion of plating to the inner walls of the through holes. Therefore, accuracy and conditions to form the through holes are complex to control, and productivity is decreased.
Especially, when the through hole has a diameter of about 0.2 mm or below, its formation takes a long time, and productivity is heavily decreased. Such problems can be remedied when a multi-layered wiring board is formed by making interlayer connection by means of conductive pillars to be described afterward.
In addition, a plating step, that electrical connection among a plurality of wiring layers is made with through holes, has to make a complex control to adjust a density of chemicals and a temperature. Besides, an apparatus for forming through holes and a facility for plating constitute a heavy burden in view of costs.
As described above, when the interlayer connection is made for the multi-layered wiring board using the through holes, productivity of the wiring substrate such as a printed wiring board (PWB) is decreased. Therefore, such a multi-layered wiring board is hard to comply with a demand for low cost.
To simplify the electrical connection among the wiring layers of the multi-layered wiring board, there is also proposed a method to connect the wiring layers with the conductive pillars. This method forms conductive pillars, such as via lands, as interlayer connections formed on a wiring circuit, and inserts the conductive pillars into the interlayer insulating layer such as a prepreg in its thickness direction to connect with the via lands formed on the opposed wiring layer.
The interlayer connection of the wiring circuit using the conductive pillars has advantages that a structure is simple, steps are not many, productivity is high, and high-density mounting can be made. However, a printed wiring board having the interlayer connection of wiring circuits using the conductive pillars has disadvantages to be described as follows.
The conductive pillars are formed on a conductive foil such as a copper foil by screen printing a plurality of times using a mask. However, no apparatus was available to print those pillars automatically. In making multiple printings by the manpower, it is difficult to keep a fixed time interval between respective printing steps, and the conductive pillars formed do not have uniform quality. Additionally an aspect ratio of the conductive pillars can be adjusted by the number of printing times, but management of the number of times to print on very many conductive foils becomes a very large burden decrease a productivity.
FIG. 19A and FIG. 19B are diagrams schematically showing a step of producing a multi-layered wiring board using conventional conductive pillars, wherein an insulating resin layer is pierced by the conductive pillars which are formed on a conductive foil.
It is seen that a conductive foil 52 such as a copper foil having conductive pillars 51 having a substantially conical shape is laminated with an insulating resin layer 53 such as a prepreg in a semi-cured state(B-stage), then heated and pressed by a plane press to pierce the insulating resin layer 53 by the conductive pillars 51. Reference numerals 91a, 91b denote press plates of the plane press. To keep the shape of the conductive pillars 51, a releasing sheet 56 is placed on the insulating resin layer 53.
However, the plane press is hard to press uniformly the entire area of the laminate. Therefore, all the conductive pillars 51 formed on the conductive foil 52 cannot pierce the insulating resin layer 53 satisfactorily due to non-uniform pressing. The conductive pillars 51 serve to make interconnection of the wiring layers of the multi-layered wiring board, so that such defective piercing is directly related to a failure of the multi-layered wiring board.
To pierce the conductive pillars 51 by the plane press, it is necessary to laminate the conductive foil 52, the insulating resin layer 53 and the releasing sheet 56 in each pressing process. After pressing, the laminate must be decomposed. Especially, when pressing is made manually, a long time is required to complete the process. Therefore, productivity of a wiring substrate is decreased.
Because of the drawbacks in the multi-layered wiring board having the interlayer connection made by the conductive pillars, it is hard to put into practical use.
Besides, when the conductive foil 52 and the insulating resin layer 53 are laminated, there is a problem that the conductive foil is readily contaminated by powder of the resin which forms the insulating resin layer.
For example, a conventional apparatus for manufacturing a printed wiring board which has the conductive foil 51 and the insulating resin layer 53 laminated has a structure as shown in FIG. 20.
For example, the insulating resin layer 53 such as a prepreg set at a predetermined position is adsorbed by aspiration heads 93 and transported so to be piled on the conductive foil 52 such as a Cu foil set at another predetermined position.
However, such a conventional apparatus has the following disadvantages.
The conventional aspiration heads partly hold the insulating resin layer by a point-to-point contact. Therefore, there is a problem that the insulating resin layer has a wrinkle when it is held and the resin forming the insulating resin layer is partly powdered to disperse to the surroundings. Furthermore, the powdered and dispersed portion of the insulating resin such as a prepreg adheres to the surface of the conductive foil and the like. As a result, an etching failure is caused or a dent is formed due to irregularities formed by the resin adhered after pressing.
In addition, the powdered prepreg produced in a step of cutting the prepreg adheres to the surface and end faces of the prepreg, and the powder has a problem of causing the same disadvantages as described above.
The invention was completed to remedy the disadvantages described above.
Specifically, it is an object of the invention to provide an apparatus for manufacturing a printed wiring board that conductive pillars can be formed automatically on a conductive foil. It is also an object of the invention to provide an apparatus for manufacturing a printed wiring board that conductive pillars having uniform properties can be formed on a conductive foil with high productivity.
The invention also aims to provide an apparatus for manufacturing a multi-layered wiring board with high productivity without having defective piercing. In addition, the invention aims to provide an apparatus for manufacturing a multi-layered wiring board that a laminate containing conductive pillars and an insulating resin layer can be pressed uniformly.
Besides, the invention aims to provide an apparatus for manufacturing a printed wiring board that a powdered portion of the prepreg can be prevented from adhering.
In order to achieve the above-described objects, the apparatus and the method for manufacturing a wiring board according to the invention has the following structure.
A first aspect of the invention relates to an apparatus for manufacturing a wiring substrate, which comprises a transporting means for transporting a sheet, the transporting means having a circuit where the sheet is circularly transported; a printing means for printing a conductive paste onto the sheet, the printing means being formed on the circuit; a counting means for counting the number of times to print the conductive paste onto the sheet; and an ejecting means for ejecting the sheet from the circuit when the counted number reaches a preset number.
By configuring as described above, conductive pillars/bumps can be automatically formed very accurately with high productivity.
The transporting means may have a conveyer combined with a direction changer. Likewise, a transporting robot may be used to transport the sheet. Besides, the transporting means may further have a first drying means on the circuit to dry the conductive paste printed by the printing means.
A memory may also be provided to store the set number for determining the number of printing times. The memory can be a non-volatile semiconductor memory such as a NAND type flash memory or an AND type flash memory.
The printing means preferably prints the conductive paste so to form a substantially conical shape on the sheet. Thus, the conductive pillars having a substantially conical shape are formed on the sheet. The conductive pillars having a substantially conical shape can easily pierce the insulating resin layer such as a prepreg in a semi-cured state(B-stage). Accordingly, productivity of a multi-layered wiring substrate is improved.
The sheet on which the conductive pillars are printed can be a conductive sheet including a conductive foil such as a copper foil or an aluminum foil. Such a conductive sheet may have a laminated structure comprises at least one conductive layer and at least one insulating layer. The insulating layer can be a prepreg, a polyimide film, a ceramics layer and the like. It is to be understood that the sheet on which the conductive pillars are printed may be a conductive layer or a wiring layer exposed to the surface of a wiring substrate.
A second aspect of the invention relates to an apparatus for manufacturing a wiring substrate, which comprises a loading means for loading at least a sheet; a means for forming conductive pillars onto the sheet; and a second drying means for drying the conductive pillars formed on the sheet; wherein the means for forming the conductive pillars comprises a transporting means for transporting the sheet, the transporting means having a first circuit and a second circuit where the sheet is circularly transported, the first circuit and the second circuit having a common part, a first printing means for printing a conductive paste on the sheet, the first printing means being formed on the first circuit, a second printing means for printing the conductive paste on the sheet, the second printing means being formed on the second circuit, a counting means for counting the number of times to print the conductive paste on the sheet, a first drying means for drying the conductive paste printed on the sheet, the first drying means being formed on the common part of the first circuit and the second circuit, a first distributing means for distributing the sheet loaded from the loading means to the first circuit and the second circuit, the first distributing means distributing the sheet ejected from the first drying means to the first circuit and the second circuit, and a second distributing means for distributing the sheet ejected from the first printing means and the sheet ejected from the second printing means to the first drying means when the counted number is less than the preset number of times, and the second distributing means distributing the sheet ejected from the first printing means and the sheet ejected from the second printing means to the second drying means when the counted number reaches the preset number.
The first distributing means distributes the conductive sheet having the conductive paste printed by the first printing means to the first circuit, and the second distributing means distributes the conductive sheet having the conductive paste printed by the second printing means to the second circuit.
In addition, the first printing means and the second printing means may be disposed symmetrically to each other on the first circuit and the second circuit. For example, conductive foils to be a pair of conductive wiring layers to hold a single layered insulating resin layer therebetween can be formed simultaneously, and a throughput can be improved.
In addition, the first printing means and the second printing means respectively print the conductive paste by using one identical mask when the conductive paste is printed onto the conductive paste already printed through the mask. Printing of the conductive paste using one and the same mask prevents displacement and allows to form fine conductive pillars accurately and uniformly.
Furthermore, the apparatus for manufacturing a wiring substrate may also have a memory for holding the preset number of times of printing the conductive paste onto the sheet.
By configuring as described above, the apparatus for manufacturing a wiring substrate according to the invention can form automatically the conductive pillars, which facilitate interlayer connection, with high productivity and high accuracy. Especially, automation facilitates to uniformly control the interval between respective printing steps, so that the conductive pillars can be formed more uniformly. Accordingly, the conductive pillars have uniform properties, and the wiring substrate having a large number of interlayer connections has improved reliability.
An apparatus for manufacturing a printed wiring board according to the invention, that an insulating resin layer is pierced by conductive pillars formed on a conductive foil, has the following structure.
Specifically, a third aspect of the invention relates to an apparatus for manufacturing a wiring substrate, which comprises a pair of rolls having a substantially parallel rotating axis, the rolls being held so as to form a gap therebetween; a means for loading a conductive sheet having a first face where conductive pillars are formed, an insulating resin sheet and a releasing sheet to the gap between the rolls so that the insulating resin sheet is interposed between the first face of the conductive sheet and the releasing sheet; and an adjusting means for adjusting the gap between the rolls so that the conductive pillars pierce the insulating resin sheet.
This pair of rolls is driven to rotate to allow the laminate to pass through the rolls under pressure. Therefore, when one of the rolls rotates clockwise, the other roll rotates counterclockwise. The apparatus for manufacturing a wiring substrate also has a driving means for driving the rolls so that the rolls have a rotating speed synchronized with a loading speed.
The individual roll may have a hollow cylindrical structure. Thus, the gap between the pair of rolls can be prevented from becoming uneven due to the expansion of rolls due to thermal expansion, and the laminate of the conductive foil, the insulating resin layer and the releasing sheet can be pressed and heated more uniformly.
The respective rolls may have therein a heating means for heating so that they have a uniform temperature distribution. For example, the distribution of surface temperature of the rolls can be limited to a small range by adjusting a winding density of a coil of an infrared heater for example. Therefore, the rolls are prevented from decentering, and the laminate can be heated and pressed more uniformly.
In addition, the releasing sheet may be loaded into the gap between the pair of rolls so that the releasing sheet has a substantially constant tension. By loading the releasing sheet into the gap between the rolls while adjusting to have a uniform tension, the releasing sheet can be prevented from having a wrinkle during pressing. Therefore, the laminate can be pressed under uniform pressure.
Furthermore, the conductive foil may be loaded so to run along one of the rolls. By adjusting the loading angle so to increase a contact area between the conductive foil and one of the rolls, the laminate is heated preliminarily before being pressed between the rolls. Thus, the insulating resin layer is pierced by the conductive pillars more uniformly and smoothly.
A fourth aspect of the invention relates to a method for manufacturing a wiring substrate, which comprises steps of loading a conductive sheet having a first face where conductive pillars are formed, an insulating resin sheet and a releasing sheet to a gap of a pair of rolls having a substantially parallel rotating axis so that the insulating resin sheet is interposed between the first face of the conductive sheet and the releasing sheet; and adjusting the gap between the rolls so that the conductive pillars pierce the insulating resin sheet.
Specifically, the method for manufacturing a printed wiring board according to the invention laminates the sheet such as a conductive foil having the conductive pillars in a substantially conical shape formed on the first face with the insulating resin sheet in a semi-cured state, and loads the laminate into the gap between the pair of rotating rolls to pierce the insulating resin sheet by the conductive pillars. The invention relates to the apparatus for manufacturing a printed wiring board that the conductive paste is printed on the conductive foil to form the conductive pillars, the insulating resin layer is laminated on the conductive foil, the laminate is heated and pressed to pierce the conductive pillars into the synthetic resin sheet, another conductive metallic foil is overlaid thereon, heated and pressed to make electrical connection of the upper and lower conductive metallic foils, and can apply the step of piercing the conductive pillars into the synthetic resin sheet to a material having a different thickness and improve a yield by varying the two rolls, the conductive bump piercing assisting material and the main material loading angle.
The apparatus for manufacturing a printed wiring board according to the invention, that the conductive foil and the insulating resin layer are laminated, has the following structure.
A fifth aspect of the invention relates to an apparatus for manufacturing a wring substrate, which comprises a holding means having a planer surface for holding an insulating resin sheet having a first face and a second face, the holding means aspirates the first face of the insulating resin sheet on the plane surface; a housing for storing a conductive foil, the housing having an opening for introducing the holding means holding the insulating resin sheet; a transporting means for transporting the holding means into the housing through the opening, the transporting means piling the insulating resin sheet onto the conductive foil; and an adjusting means for adjusting a pressure inside the housing so that the pressure inside the housing is higher than a pressure outside the housing.
Furthermore, the apparatus for manufacturing a wring substrate may have a cleaning means, which is formed outside of the opening of the housing and cleans the surface of the prepreg adsorbed by the holding member and its opposite surface. In addition, the cleaning means having at least an aspirating slit elongated with the opening, for example.
Furthermore, the apparatus for manufacturing a wring substrate may have a cleaning means, which is formed outside of the opening of the housing and cleans the surface of the prepreg adsorbed by the holding member and its opposite surface.
By configuring as described above, the apparatus for manufacturing a wiring substrate according to the invention can hold the resin sheet such as a prepreg without causing a wrinkle. In addition, no powdered resin is dispersed to the surroundings, so that a failure due to the dispersed powder can be decreased during laminating.
According to the present invention, productivity of a wiring substrate can be improved substantially, and reliability of a wiring substrate can be improved.